1. Field of the Invention
This invention relates to an apparatus for forming a glass product and a method for forming a glass product such as a panel for a cathode ray tube (CRT).
2. Discussion of Background
Conventionally, as a press forming device of a glass product such as a panel or a funnel for a CRT, as shown in FIG. 3, a device is known in which a plurality of bottom molds are arranged on a disk-like index table 13, in its circumferential direction, and the index table to which the bottom molds are fixed, indexes (rotates by every predetermined angle) around the center axis thereof, successively in the order of the positions of generally the glass gob feeding device 11, the press forming device 10, the cooling device 1, the shell mold removing device 2, the cooling device 3, the formed body removing device 6, and the shell mold attaching device 8.
The conventional press forming device has following problems, in view of promoting the quality of the formed body such as dimensional accuracy of the formed body. The dimension and the quality of the formed body is controlled by heating with a burner or air cooling or water cooling of the surroundings of the molds corresponding with the nonuniformity of the cooling of the formed body, so that the temperature distribution of the formed body becomes uniform in cooling and solidifying the formed body in the mold after press forming. In this case, since arrangement of the molds is concentric, a sufficient space is required for the temperature measurement, the heating and the cooling, to accurately control the temperature of the molds on the center axis side of the index table. For that reason, the diameter of the index table has to be enlarged, which magnifies the facility, and which worsens the efficiency in view for the maintenance and the power thereof. Furthermore in the conventional press forming device, since the molds are fixed on the index table, the accurate adjustment of the relative position between a plunger of the press forming device and the molds is difficult, due to the thermal expansion of the index table. The enlargement of the index table is not desirable also in this respect. The adjustment of the position of the glass gob feeding, is performed by moving the whole body of the index table. Therefore a large scale facility for adjustment is required.
Furthermore, since the conventional press forming device has only one press forming device, the index time is restricted by the press forming time. Therefore, in switching the product kinds, the glass quantity per unit time necessary for press forming the formed body, has a variation, and the furnace operation becomes unstable.
In case of forming a panel for a CRT using a forming device which indexes simultaneously a plurality of molds, as mentioned above, when a pin welding operation for fixing the shadow mask on the formed body before it is removed from the mold, is required, although it is convenient that the glass temperature is elevated, since the welding time requires 10 seconds or more, the indexing stop time is extended, and the productivity is considerably lowered. For that reason, as shown in FIG. 4, the press forming step and the pin welding step have to be separated, which magnifies the facility and makes a production cost high.
In FIG. 4, a reference numeral 11 designates a glass gob feeding device, 12, a slow cooling furnace, 14, an index table, 15, a conveyor for panel transportation, and 16, a pin welding device.
Conventionally, the pins for fixing the shadow mask are welded to the inner surface of the panel after the press forming, by a burner heating or by an electromagnetic induction heating, which is a process separate with the press forming step, after a molten glass lump called glass gob is dropped on the mold, press-formed, cooled, and removed from the mold. However the pin welding is performed after the temperature of the panel after removed from the mold, is lowered. Therefore much time is required for the pin welding. Moreover, when the pin welding is performed, a new strain is introduced in the portion of the panel, and the shape of the panel at the welded portion of the pin is changed, which restricts the improvement of the quality.